LTC3586-1_15 Datasheet, PDF (15/36 Pages) Linear Technology – High Efficiency USB Power Manager with Boost, Buck-Boost and Dual Bucks

LTC3586/LTC3586-1
OPERATION
The current at CLPROG is a fraction (h_{CLPROG–1}) of the
V_BUS current. When a programming resistor and an av-
eraging capacitor are connected from CLPROG to GND,
the voltage on CLPROG represents the average input
current of the PowerPath switching regulator. When the
input current approaches the programmed limit, CLPROG
reaches V_CLPROG, 1.188V and power out is held constant.
The input current limit is programmed by the I_LIM0 and
I_LIM1 pins to limit average input current to one of several
possible settings as well as be deactivated (USB Suspend).
The input current limit will be set by the V_CLPROG servo
voltage and the resistor on CLPROG according to the fol-
lowing expression:
( ) ^I_VBUS
= I_VBUSQ
+
V_CLPROG
R_CLPROG
•
h_CLPROG + 1
Figure 1 shows the range of possible voltages at V_OUT as
a function of battery voltage.
Ideal Diode from BAT to V_OUT
The LTC3586/LTC3586-1 have an internal ideal diode as
well as a controller for an optional external ideal diode.
The ideal diode controller is always on and will respond
quickly whenever V_OUT drops below BAT.
If the load current increases beyond the power allowed
from the switching regulator, additional power will be
pulled from the battery via the ideal diode. Furthermore,
if power to V_BUS (USB or wall power) is removed, then
all of the application power will be provided by the bat-
tery via the ideal diode. The transition from input power
to battery power at V_OUT will be quick enough to allow
only the10µF capacitor to keep V_OUT from drooping. The
ideal diode consists of a precision amplifier that enables
a large on-chip P-channel MOSFET transistor whenever
the voltage at V_OUT is approximately 15mV (V_FWD) below
the voltage at BAT. The resistance of the internal ideal
diode is approximately 180mΩ. If this is sufficient for the
application, then no external components are necessary.
However, if more conductance is needed, an external
P-channel MOSFET transistor can be added from BAT to
V_OUT. See Figure 2.
When an external P-channel MOSFET transistor is present,
the GATE pin of the LTC3586/LTC3586-1 drive its gate for
automatic ideal diode control. The source of the external
P‑channel MOSFET should be connected to V_OUT and the
drain should be connected to BAT. Capable of driving a
1nF load, the GATE pin can control an external P-channel
MOSFET transistor having an on-resistance of 40mΩ or
lower.
4.5
4.2
3.9
NO LOAD
3.6
3.3
300mV
3.0
2.7
2.4
2.4 2.7 3.0 3.3 3.6 3.9 4.2
BAT (V)
3586 F01
Figure 1. V_OUT vs BAT
2200
2000
1800
VISHAY Si2333
OPTIONAL EXTERNAL
IDEAL DIODE
1600
1400
1200
1000
LTC3586/
LTC3586-1
IDEAL DIODE
800
600
ON
400
SEMICONDUCTOR
MBRM120LT3
200
0
0 60 120 180 240 300 360 420 480
FORWARD VOLTAGE (mV) (BAT – V_OUT)
3586 F02
Figure 2. Ideal Diode Operation
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